HIIT versus Cardio

HIIT versus Cardio

HIIT versus Cardio


The benefits and drawbacks of HITT (Intervals) and steady state cardio

For decades bodybuilders have used low intensity cardio training during their dieting phase to get in shape for contests. Without access to some of the advances in training, nutrition, and supplements in recent years, these bodybuilders consistently got in great shape time after time with a low level of body fat and a very small waist seen among many athletes from that era. Why then has there been a trend for steady state, low intensity cardio to be dismissed as a short cut to getting fat and dropping muscle?

HIIT versus cardio

In the fitness community we encounter a lot of trends, with certain things becoming fashionable for a time before someone rails against it, leading to an inevitable backlash against what was formerly very popular. Think of the number of different fitness crazes that last for a couple of years before sinking into obscurity. This no doubt explains why many gyms feel the need to change their equipment types all the time and constantly introduce new gimmicks.

Today, high intensity interval training (HIIT) is often proclaimed to be superior to steady state cardio in every way. Proponents argue that HIIT leads to greater fat loss and less muscle tissue loss than regular cardio. To determine the extent to which this is true we must first define the two forms of training then take a look at the benefits and costs associated with each.

Defining steady state cardio and HIIT

As the name suggests, steady state cardio involves maintaining a low to medium intensity of effort for a prolonged duration. Many people performing this type of training have tended to focus on getting their heart rates up to a supposed ‘fat burning zone’. As we will discover, the notion of a particular fat burning zone is based in a false reading of the research. However, this notion has been promulgated for so long that many people now accept it as fact.

Generally speaking, steady state cardio involves keeping the heart rate in the range of 100-150bpm, typically for periods of 20-60 minutes.

On the other hand, HIIT (high intensity interval training) involves intermittent high-intensity activity interspersed with periods of zero to low activity and repeated for a number of sets/intervals.

Technically, the phrase ‘interval training’ applies to activities such as weight training and to the type of workout performed by many competitive 100m sprinters. The main things that distinguish interval training are the emphasis on incomplete recovery and the goal of improving performance, whereas HIIT is used specifically to improve body composition.

A typical HIIT workout will involve 10-60 second bursts of high intensity activity employing a variety of modalities such as running, cycling, rowing and stair climbing. These are interspersed with rest periods of anywhere between 10 and 240 seconds. Typically a work:rest ratio of 1:1-1.5 is employed.

Now that we are on the same page regarding what constitutes steady state cardio versus HIIT, it is time to consider the relative costs and benefits associated with each as well as some of the arguments that can be made in support of both types of training.

Steady State Cardio Benefits

Less taxing. On the face of it, steady state cardio is a lot easier to perform, making it a better choice for people who are unfit or already perform a lot of high intensity activity. The former group would be unable to train at a sufficiently high intensity to get anything out of intervals in the first place. For the latter group, athletes performing heavy leg sessions may find that including intervals in their training could impede their recovery as well as being more neurally taxing than steady state cardio.

Burns more calories. Although interval sessions burn more calories per unit of time, the ability to perform cardio for longer time periods means that more total calories can be burned during steady state cardio.

Frequency. It is easier to recover after performing lower-intensity exercise so cardio can be performed more frequently than intervals, and potentially on a daily basis.

Steady State Cardio Drawbacks

Muscle loss. There is little doubt that performing a lot of endurance work leads to metabolic adaptations that bias the body to burning off muscle tissue. For evolutionary reasons, it makes sense to trim muscle mass if seeking great endurance levels. Related to the loss in muscle mass is the promotion of slow twitch muscle fibres and accelerated loss of fast twitch muscle fibres. For an athlete involved in a sport requiring high levels of strength or speed this is a big issue.

Boring. Long sessions on the bike or rowing machine can be anathema to anaerobic athletes used to lifting using high intensity techniques. Although a lot of endurance buffs enjoy their runs it seems to be the case that cardio is only enjoyable for those who naturally gravitate towards it. This is an issue if a strength athlete fails to perform his cardio due to boredom.

Chronic injuries. Pounding the pavement is associated with a higher degree of joint injuries. To a certain extent, overuse injuries will occur during any physical activity including in the weight room and the way to help avoid them is to rotate your exercises and cardio choices.

Interval Training (HIIT) Benefits

Time efficient. Intervals can be completed in as little as ten minutes or less making them a very time efficient form of training.

High intensity. The fact that HIIT means performing at maximal effort makes it somewhat more similar to weight training than cardio, a feature that makes it more attractive to most strength athletes who like a challenge but get bored easily.

Metabolic similarities. Because HIIT tends to utilise similar exercise intensities and durations as regular weight training, it’s easier to implement for athletes who want to match the motor qualities of their cardio with what they do in the gym. Nutritionally speaking, both HIIT and weight training will respond favourably to supplements such as creatine and beta alanine, for instance.

Enhances fat burning. Compared to regular cardio, intervals are associated with enhanced utilisation of fat as a fuel store.

Increased EPOC. EPOC means excess post exercise oxygen consumption. In layman's terms, it means the number of calories you burn after your exercise session is completed. Intervals burn more calories after working out than does regular cardio.

Enhanced production of fat burning hormones. Compared to normal cardio, HIIT leads to greater release of endogenous fat burning hormones such as adrenaline and noradrenaline, which are associated with greater thermogenesis. In addition, the action of these compounds can lead to the suppression of appetite commonly seen with high intensity activity.

Interval Training (HIIT) Drawbacks

Unsuitable for some. Intervals are unlikely to be a good fit for those who are either not very fit or not used to working hard in the gym, as such individuals will be unable or unwilling to push themselves to the degree needed to make this form of training work for them.

Fewer calories burned. As noted, the average interval session burns fewer calories than a cardio session, which can be performed both for longer and more frequently.

Recovery issues. When it comes to leg activity, it is difficult to perform intervals at a suitable intensity to elicit fat loss effects whilst avoiding overtraining. Those who attempt to do high intensity leg work can often end up feeling sore all week long.

Acute injuries. Whilst enormous amounts of steady state cardio can cause overuse injuries, the intensity of intervals can easily lead to acute injuries such as hamstring pulls or sprains and muscle tears. For heavier people in particular, the stresses imposed on joints by performing sprints correlates with a heightened risk of injury.

Low frequency. As stated previously, intervals cannot be performed more than two to three times a week at the very most, maybe less if you are working your legs hard in the gym. Intervals are therefore not ideal for people who want to train daily as part of their routine (e.g. those who find that this helps them stick to their plan).

Pain. Make no mistake, provided intervals are performed properly they hurt and some people are quite simply unable to tolerate the pain needed to obtain results using this method.

Still not sure which form of training would be best for you? Check out Part 2 for more information on interval training’s EPOC and discover whether or not this makes it superior to steady state cardio.

Is sprinting better for bodybuilders than distance running?

It is a commonly held belief in many bodybuilding circles that steady state cardio causes muscle tissue loss whilst HIIT (high intensity interval training) targets fat stores only and might even lead to some muscle gain. In the case of running, proponents often support this view with the argument that most marathon runners have a super slim physique while many professional sprinters look like Greek gods, hence bodybuilders should perform intervals.

Is interval running really a better option for bodybuilders than steady state cardio, or is the matter more complex than this line of reasoning implies?

Street marathon

The HIIT versus cardio debate

In Part 1 of our series on cardio and HIIT, we looked at some of the benefits and costs associated with each form of training. We should add that this was done purely from the standpoint of their relative impact on body composition rather than on aerobic or anaerobic performance.

In Part 2 we questioned the popular belief that interval training is superior to steady state cardio by virtue of the EPOC or “afterburn” effect, which advocates give as the main reason for the superiority of HIIT. Upon closer examination, we concluded that the number of calories burned from HIIT are only slightly more than those burned from regular cardio.

Once one adjusts for the fact that steady state cardio can be performed more frequently and for longer than interval training, the weekly EPOC generated via steady state cardio is actually likely to be greater than that generated via interval training.

Another question that splits opinion amongst athletic trainers is which of these forms of cardio, if either, is more likely to lead to muscle loss. Many argue that HIIT is better because it’s a high-intensity form of exercise, but does this reasoning hold up in practice?

The Issue with Comparing Marathon Runners and Sprinters

SprinterTo the average person, comparing the slender marathon runner with the muscular sprinter is a pretty good argument in favour of HIIT. However, to those in the know it is a gross misrepresentation of both the form of cardio used by bodybuilders and the type of interval training conducted by sprinters. In other words, sprinters' interval training looks nothing like what bodybuilders espousing intervals do.

Similarly, while the average bodybuilder looking to drop a little fat might perform 30-60 mins of cardio in conjunction with a resistance training program many endurance athletes perform several hours’ worth of aerobic training with no resistance work at all.

So neither the sprinter nor the marathon runners training is in any way comparable to either the interval OR steady state cardio performed by bodybuilders.

Arguing that any bodybuilder who performs steady state cardio is destined to end up with the physique of an endurance athlete completely misrepresents the actual training methods used by both. This point of view also fails to account for the differences in phenotype, nutrition and use of ergogenics between these two populations.

How Sprinters Perform Intervals is Nothing like Bodybuilders Doing HIIT

Similarly, many of those who make the case for HIIT employ a distorted view of the actual training done by elite sprinters. If we look at the typical HIIT program, it will tend to involve a work to rest ratio of 1:1 with some, including the famous Tabata Protocol, demanding a work to rest ratio of 2:1. Very strenuous training without a doubt.

By contrast, elite 100m sprinters will typically sprint at maximum pace for no longer than 100m, which means their work times will be around 10 to 12 seconds. After such exertion they will typically rest for up to 15 minutes before the next set. That means that for a 10 second sprint their work to rest ratio would be 1:90! This is closer to powerlifting for 1-3 reps than it is to anything resembling HIIT as practiced by bodybuilders. 

But what about 400m runners, for whom keeping pace requires speed as well as excellent aerobic and anaerobic endurance? To achieve this, training typically resembles that of a short distance sprinter but with a much larger component of relatively long-distance runs of 300-800m.

While distances of these kinds bear a closer similarity to the ones seen in HIIT, the difference with a 400m runner is that, contrary to popular belief, the vast majority of this work is performed at sub-maximal intensity. For instance, Michael Johnson, the 400m world record holder, was known to run for over 20 minutes in his off season to help build his aerobic endurance.

 “The 400m is much harder to pace (than the 200) since nobody can go out and run 400 meters full-speed from the gun.” - Michael Johnson

If HIIT is a superior form of training for fat loss as its advocates claim, we need a better argument than the flawed comparison that is comparing the physiques of marathon runners with sprinters and assuming that either trains anything like how a bodybuilder would perform cardio.

Next up we will look at the effects of steady state cardio on performance.

While we saw in part 3 that the impact of HIIT on body composition is overplayed based on misleading references to the differences in the physiques of track sprinters versus endurance runners, there is also the fact that the few studies showing that intervals are associated with slight muscle gains were conducted on untrained subjects with no weight training background. Once we add the fact that most of the people reading this will be performing weight training for muscle building in addition to any cardiovascular work being performed then the relevance of HIIT for building muscle drops to zero. Aside from its effect on body composition we have to consider the effects of HIIT and steady state cardio on performance. We will look first at steady state cardio.

Steady State Cardio & Performance

Steady state cardio has been shown in research (1,2) to counteract the effects of strength training due to the fact that the two activities produce differing molecular adaptations in the body, with the activation of AMPK by endurance exercise inhibiting the activity of the key anabolic signalling protein mTOR which is critical for the muscle building effects associated with weight training. In addition, the Australian research study shows that performing an acute bout of endurance training before weight training blunts the activity of anabolic hormones such as IGF-1 and MGF while performing a bout of cardio after weight training was shown in the same study to increase the production of genes associated with muscle breakdown. It was notable that in this particular study the actual endurance workout performed was not particularly excessive being only 30 minutes in length and 70% Vo2 peak. Although other research has in the past showed that performing cardio after weights enhances fat loss (3), the Australian research did not track performance or body composition, only measuring the levels of various signalling hormones associated with muscle anabolism and catabolism respectively. It should also be noted that the researchers in this study failed to provide participants in the study with any nutritional support for 3 hours after their exercise bout which would definitely have contributed to a negative environment for muscle growth.

Steady State Cardio – Empirical Evidence

Setting aside the research for a moment, we can see from the real world that excessive endurance training is associated with much lower muscle mass in athletes in sports requiring high endurance levels although even then we see that in some sports such as cycling, the riders will often display pronounced muscle hypertrophy despite the high degree of endurance activity performed.

Away from endurance sports it is worthwhile looking at athletes in mixed sports requiring both anaerobic and aerobic fitness as these will often utilise both forms of training in a more balanced ratio than seen with either competitive strength athletes or endurance athletes. Athletes in such sports will often structure their use of endurance and weight training through the year in cycles and for the most part, will employ endurance training including steady state cardio (but also intervals) in increasing amounts closer to the start of their season whereas weight training is emphasised during the off season. What tends to happen is that they increase their strength and muscle mass during the off season and then during the in-season only manage to maintain their strength levels (or try to lower the decline in strength that can occur especially during the in-season of contact sports).

Based on research and real world outcomes there is both theoretical and empirical support to suggest combining endurance training with weight training can have negative consequences for both performance and body composition. A sensible strategy to mitigate this would be to ensure provision of adequate nutrition especially BCAA's during the training session as well as to try to keep exercise sessions for cardio and weights separate to avoid sending mixed signals to the body. Other than this, for anyone who emphasises weight training as a priority, the intensity, duration and frequency of steady state cardio should be carefully monitored to prevent unnecessary muscle breakdown. Moving on from the effects of steady state cardio it will be time to discuss how intervals can impact performance in the gym in part 5, before we wrap up this series with a conclusion and make some recommendations for different kinds of subjects.

We have previously discussed in our series of articles comparing HIIT (also known as interval training) and steady cardio both the relative benefits and costs associated with each approach, a discussion on the relative impact of EPOC for HIIT, looked at why comparing sprinters with marathon runners is a misleading way to present HIIT training, and most recently looked at the effects of steady state cardio on performance and body composition by looking at both research and empirical evidence.

HIIT - Research On Effects On Performance And Body Composition

HIIT has been shown in some research including the famous one conducted by Tremblay to have a slight muscle building benefit but as was noted earlier, these studies were conducted on beginners for whom any high intensity activity may be liable to produce a muscle building effect. This is a long way from saying that it will have an effect on experienced athletes with a history of resistance training behind them.

Research on high intensity training has consistently shown that it is associated with an entirely different metabolic response to low intensity training with a relatively new study (1) showing that interval training led to significant increases in anabolic hormones including testosterone, growth hormone, and IGF-1 when performed by twelve elite handball players.

Studies such as this have been repeated by others and together they help paint a picture of interval training inducing a positive hormonal response which is beneficial for body composition benefits and building muscle. Despite this we have to be careful of extrapolating studies showing beneficial hormonal effects associated with interval training in non-weight training subjects and assume it means bodybuilders should employ intervals unilaterally. As we have already discussed in our series, for the purposes of generating a large caloric deficit for instance, steady state cardio is a superior tool albeit one with a negative relationship to weight training. Set against this other research shows that interval training can produce similar metabolic adaptations to steady state cardio (2) in a much shorter period of time which certainly makes intervals a useful strategy for athletes needing to rapidly improve their fitness in a short time frame.

The one major issue with all the research though is that it tends to look at isolated, short term studies in beginners or, if they use trained athletes, they tend to be ones whose primary training focus does not require the use of weight training. In addition, it should be noted that the types of intensities used in these studies are rarely used by elite athletes in any sport for longer than a few weeks due to the rapid habituation that occurs not to mention the risk of overtraining associated with a high volume of interval training.

Empirical Evidence for HIIT

While there is a good deal of anecdotal not to mention research supporting the usage of HIIT training for accelerating fat loss its usage at the top levels of sport is relatively low and, as discussed already, the way it is suggested HIIT is performed tends to be very dissimilar to how any athlete on the track trains. We have already mentioned that we should be wary of applying data from untrained, non-weight training subjects and uncritically applying them to strength athletes so will discuss this in greater detail now.

One of the biggest drawbacks with interval training is that it is both neurologically demanding causing a big drain on the central nervous system but can also cause profound soreness especially in the legs, something which is exacerbated when bodybuilders use sprint training to conduct HIIT. Among elite athletes who sequence interval training into their routines it is rare to see it performed more than twice a week although shorter distance sprint athletes will go up to three a week.

How Bodybuilders Perform Intervals Cannot be Compared to Athletes 

Even then, these athletes will as we covered in part 3, utilise much longer rest intervals compared to that seen by those practising HIIT training. In addition, to a man (or woman) they will be following a high carbohydrate diet which is essential both for fueling exercise performance but also enhancing recovery from training. Given this how is it that many bodybuilders who are using HIIT attempt to do so while following a calorie restricted, and often carb constricted diet, while at the same time using shorter rests than world class athletes while attempting to perform intervals more frequently than track athletes (some gurus suggest daily intervals!), and with a higher volume of work. In addition, unlike track athletes, for bodybuilders the prime motivation for their training is to build a large degree of muscle mass which means they will already be doing more weight training than athletes involved in other sports.

What does this spell out? Quite clearly, anyone who is using intervals indiscriminately is going to face serious recovery issues especially in their leg training which is going to have the consequence of impeding muscle and strength gains massively. Compared to performing steady state cardio 3-4 times a week, anyone performing even a fairly restricted HIIT program for that number of times is going to really struggle to avoid their performance in the gym, not to mention their muscle mass from dropping off. If we add to this the fact that unlike athletes, the vast majority of bodybuilders employing HIIT are not used to this type of training so more likely to get sore/injured, and more likely to be using it while dieting, then it is clear that using intervals while training simultaneously for bodybuilding can be very damaging to physiques.

Rather than accepting uncritically the argument that intervals are superior we need to look carefully at our goals when training, and, if building muscle mass or maintaining it is a concern, then the usage of intervals needs to be thought about much more carefully than most do currently.


  1. Nader (2006): Concurrent strength and endurance training: from molecules to man.
  2. Coffey VG (2009): Consecutive bouts of diverse contractile activity alter acute responses in human skeletal muscle.
  3. Goto K (2007): Effects of resistance exercise on lipolysis during subsequent submaximal exercise.